Lubricating oil compositions for internal combustion engines generally contain a variety of additives to reduce or control deposits, wear, corrosion, etc. Similarly, liquid hydrocarbon fuels for internal composition engines, at a minimum, contain additives which control or reduce the formation of deposits. The present invention is concerned with compositions useful as dispersants or deposit inhibitors.
In lubricating oils, dispersants function to control sludge, carbon, and varnish produced primarily by the incomplete oxidation of the fuel, or impurities in the fuel, or impurities in the base oil used in the lubricating oil composition. Dispersants also control viscosity increase due to the presence of soot in diesel engine lubricating oils.
Deposit inhibitors in fuel control or reduce engine deposits also caused by incomplete combustion of the fuel. Such deposits can form on the carburetor parts, throttle bodies, fuel injectors, intake ports, and valves. Those deposits can present significant problems, including poor acceleration and stalling, and increased fuel consumption and exhaust pollutants.
One of the most effective classes of lubricating oil dispersants and fuel deposit inhibitors is polyalkylene succinimides. In some cases, the succinimides have also been found to provide fluid-modifying properties, or a so-called viscosity index credit, in lubricating oil compositions. This results in a reduction in the amount of viscosity index improver, which would be otherwise required. A drawback of succinimide dispersants is that they have generally been found to reduce the life of fluorocarbon elastomers. In general, for a given succinimide dispersant, a higher nitrogen content gives better dispersancy but poorer fluorocarbon elastomer compatibility.
Therefore, as well as improving the dispersancy and VI credit properties of polyalkylene succinimides, it would be desirable to improve the fluorocarbon elastomer compatibility of such dispersants. It would further be desirable to improve the stability of polyalkylene succinimides, particularly hydrolytic stability and shear stress stability. It would also be desirable to improve soot dispersancy, especially where the lubricating oil is intended for use in diesel engine crankcases.
Polyalkylene succinimides are generally prepared by the reaction of the corresponding polyalkylene succinic anhydride with a polyalkyl polyamine. Polyalkylene succinic anhydrides are generally prepared by a number of well-known processes. For example, there is a well-known thermal process (see, e.g., U.S. Pat. No. 3,361,673), an equally well-known chlorination process (see, e.g., U.S. Pat. No. 3,172,892), a combination of the thermal and chlorination processes (see, e.g., U.S. Pat. No. 3,912,764), and free radical processes (see, e.g., U.S. Pat. Nos. 5,286,799 and 5,319,030). Such compositions include one-to-one monomeric adducts (see, e.g., U.S. Pat. Nos. 3,219,666 and 3,381,022), as well as "multiply adducted" products, adducts having alkenyl-derived substituents adducted with at least 1.3 succinic groups per alkenyl-derived substituent (see, e.g., U.S. Pat. No. 4,234,435).
U.S. Pat. Nos. 3,361,673 and 3,018,250 describe the reaction of an alkenyl- or alkyl-substituted succinic anhydride with a polyamine to form alkenyl or alkyl succinimide lubricating oil dispersants and/or detergent additives.
U.S. Pat. No. 4,612,132 teaches that alkenyl or alkyl succinimides may be modified by reaction with a cyclic or linear carbonate or chloroformate such that one or more of the nitrogens of the polyamine moiety is substituted with a hydrocarbyl oxycarbonyl, a hydroxyhydrocarbyl oxycarbonyl, or a hydroxy poly(oxyalkylene) oxycarbonyl. These modified succinimides are described as exhibiting improved dispersancy and/or detergency in lubricating oils.
U.S. Pat. No. 4,747,965 discloses modified succinimides similar to those disclosed in U.S. Pat. No. 4,612,132, except that the modified succinimides are described as being derived from succinimides having an average of greater than 1.0 succinic groups per long chain alkenyl substituent.
An article by S. T. Roby, R. E. Kornbrekke, and J. A. Supp "Deposit Formulation in Gasoline Engines, Part 2, Dispersant Effects on Sequence VE Deposits" JOURNAL OF THE SOCIETY OF TRIBOLOGISTS AND LUBRICATION ENGINEERS, Vol. 50, 12, 989-995 (December 1994) teaches that the length of the dispersant alkyl side chain influences deposit control performance, and that, at the same nitrogen level, the low molecular weight (side chain 1000 daltons) dispersants that were tested were poorer than the tested high molecular weight (side chain 2000 daltons) succinimide dispersants.
U.S. Pat. No. 4,234,435 teaches a preferred polyalkene-derived substituent group with a number average molecular weight (M.sub.n) in the range of 1500-3200. For polybutenes, an especially preferred M.sub.n range is 1700-2400. This patent also teaches that the succinimides must have a succinic ratio of at least 1.3. That is, there should be at least 1.3 succinic groups per equivalent weight of polyalkene-derived substituent group. Most preferably, the succinic ratio should be from 1.5 to 2.5. This patent further teaches that its dispersants also provide an improvement in viscosity index. That is, these additives impart fluidity modifying properties to lubricant compositions containing them. This is considered desirable for use in multigrade lubricating oils but undesirable for single-grade lubricating oils.
Polyamino alkenyl or alkyl succinimides and other additives useful as dispersants and/or detergents, such as Mannich bases, contain basic nitrogen. While basicity is an important property to have in the dispersant/detergent additive, it is believed that the initial attack on fluorocarbon elastomer seals used in some engines involves attack by the basic nitrogen. This attack leads to the loss of fluoride ions, and eventually results in cracks in the seals and loss of other desirable physical properties.
A variety of post-treatments for improving various properties of alkenyl succinimides are known to the art, a number of which are described in U.S. Pat. No. 5,241,003.
Example 2 of U.S. Pat. No. 5,266,186 discloses the preparation of dispersants by reacting certain polyisobutenyl-succinic anhydride adducts (see footnote 2 of Table 2) with ethylenediamine, followed by reaction with a maleic anhydride/alpha-olefin copolymer. The patent teaches that, by functioning as an iron sulfide dispersant, the product is useful to inhibit sludge deposits in refinery processing equipment caused by the heat treatment of hydrocarbon feed stocks.
U.S. Pat. No. 5,112,507 discloses a polymeric ladder type polymeric succinimide dispersant in which each side of the ladder is a long chain alkyl or alkenyl, generally having at least about 30 carbon atoms, preferably at least about 50 carbon atoms. The dispersant, described as having improved hydrolytic stability and shear stress stability, is produced by the reaction of certain maleic anhydride-olefin copolymers with certain polyamines. The patent further teaches that the polymer may be post-treated with a variety of post-treatments, and describes procedures for post-treating the polymer with cyclic carbonates, linear mono- or polycarbonates; boron compounds (e.g., boric acid), and fluorophosphoric acid and ammonia salts thereof.
U.S. Pat. Nos. 5,334,321 and 5,356,552 disclose certain cyclic carbonate post-treated alkenyl or alkylsuccinimides having improved fluorocarbon elastomer compatibility, which are preferably prepared by the reaction of the corresponding substituted succinic anhydride with a polyamine having at least four nitrogen atoms per mole.
European Application, EP 0 682 102 A2 discloses a process which comprises reacting: a copolymer of an olefin and maleic anhydride, an acyclic hydrocarbyl-substituted succinic acylating agent, and an alkylene polyamine. These products are described as useful in lubricating oil compositions as additives for use as dispersants having viscosity index improver properties.
U.S. Pat. No. 3,819,660, titled "Alkenylsuccinic Anhydride Preparation," discloses the suppression of fumaric acid sublimation and tar formation during reaction of a 168 to 900 molecular weight alkene with maleic anhydride and increased yield of alkenylsuccinic anhydride by using a catalytic amount of p-alkylbenzenesulfonic acid.
U.S. Pat. No. 4,235,786, titled "Process for Producing Oil-Soluble Derivatives of Unsaturated C.sub.4 -C.sub.10 Dicarboxylic Acid Materials," discloses the Ene reaction of an unsaturated C.sub.4 -C.sub.10 dicarboxylic acid and a C.sub.30 -C.sub.700 olefin carried out in the presence of an oil-soluble, strong organic acid having a pK.sub.a of less than 4, such as sulfonic acid.
U.S. Pat. No. 5,777,025, titled "Process for Preparing Polyalkenyl Substituted C.sub.4 to C.sub.10 Dicarboxylic Acid Producing Materials," discloses a process for preparing a polyalkylene derivative of a monounsaturated C.sub.4 carboxylic acid by running the reaction in the presence of a sediment-inhibiting amount of an oil-soluble hydrocarbyl substituted sulfonic acid.
European Patent Application 0 542 380 A1, titled "Process for the preparation of polyalkenyl derivatives of unsaturated dicarboxylic acid materials," discloses a process for the preparation of a polyalkenyl derivative of a monoethylenically unsaturated C.sub.4 -C.sub.10 dicarboxylic acid material wherein the ratio of dicarboxylic acid moieties per polyalkenyl chain is less than 1.2:1. That process comprises reacting a polyalkene having a M.sub.n in the range of 950 to 5000 with a monoethylenically unsaturated C.sub.4 -C.sub.10 dicarboxylic acid material in a mole ratio of greater than 1:1 at a temperature in the range of 150.degree. to 260.degree. C. in the presence of a polyaddition-inhibiting amount of a sulfonic acid.